U.S. patent number 10,580,547 [Application Number 15/501,984] was granted by the patent office on 2020-03-03 for scintillator panel and radiation detector.
This patent grant is currently assigned to Toray Industries, Inc.. The grantee listed for this patent is TORAY INDUSTRIES, INC.. Invention is credited to Hideyuki Fujiwara, Naohide Itsuki, Takahiro Tanino.
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United States Patent |
10,580,547 |
Tanino , et al. |
March 3, 2020 |
Scintillator panel and radiation detector
Abstract
Provided is a scintillator panel which can be more easily and
conveniently manufactured at a low cost and which has a high
luminance and a high sharpness. The scintillator panel according to
the present invention includes: a substrate; barrier ribs placed on
the substrate; and a phosphor packed into cells separated by the
barrier ribs, the phosphor having a porosity of 20% or less and
having a grain boundary.
Inventors: |
Tanino; Takahiro (Otsu,
JP), Fujiwara; Hideyuki (Otsu, JP), Itsuki;
Naohide (Otsu, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
TORAY INDUSTRIES, INC. |
Tokyo |
N/A |
JP |
|
|
Assignee: |
Toray Industries, Inc. (Tokyo,
JP)
|
Family
ID: |
55263806 |
Appl.
No.: |
15/501,984 |
Filed: |
August 3, 2015 |
PCT
Filed: |
August 03, 2015 |
PCT No.: |
PCT/JP2015/071931 |
371(c)(1),(2),(4) Date: |
February 06, 2017 |
PCT
Pub. No.: |
WO2016/021540 |
PCT
Pub. Date: |
February 11, 2016 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20170236609 A1 |
Aug 17, 2017 |
|
Foreign Application Priority Data
|
|
|
|
|
Aug 8, 2014 [JP] |
|
|
2014-162144 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G21K
4/00 (20130101); G01T 1/20 (20130101); G01T
1/2002 (20130101); G01T 1/202 (20130101); A61B
6/00 (20130101) |
Current International
Class: |
G01T
1/20 (20060101); G01T 1/202 (20060101); G21K
4/00 (20060101); A61B 6/00 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
01191084 |
|
Aug 1989 |
|
JP |
|
2004317300 |
|
Nov 2004 |
|
JP |
|
2011007552 |
|
Jan 2011 |
|
JP |
|
2011207937 |
|
Oct 2011 |
|
JP |
|
2011257339 |
|
Dec 2011 |
|
JP |
|
5060871 |
|
Oct 2012 |
|
JP |
|
WO 2012161304 |
|
Nov 2012 |
|
JP |
|
5188148 |
|
Apr 2013 |
|
JP |
|
2014106022 |
|
Jun 2014 |
|
JP |
|
2012161304 |
|
Nov 2012 |
|
WO |
|
Other References
International Search Report and Written Opinion for International
Application No. PCT/JP2015/071931, dated Sep. 8, 2015, 7 pages.
cited by applicant.
|
Primary Examiner: Kim; Kiho
Attorney, Agent or Firm: RatnerPrestia
Claims
The invention claimed is:
1. A scintillator panel comprising: a substrate; barrier ribs
placed on the substrate; and a phosphor packed into cells separated
by the barrier ribs, the phosphor being a compound selected from
the group consisting of CsI:Tl, NaI:Tl and SrI2:Eu, the phosphor
having a porosity of 20% or less and having a grain boundary,
wherein the phosphor has an average particle size of 20 to 200
.mu.m, and wherein the grain boundary is a discontinuous boundary
surface generated between a plurality of crystals of the phosphor
by observing a cross-section of the phosphor using EBSD (electron
back scatter diffraction patterns) method.
2. The scintillator panel according to claim 1, wherein the
phosphor has a porosity of 0.1% or more.
3. The scintillator panel according to claim 1, wherein the barrier
rib includes an inorganic substance, and the barrier rib has a
porosity of 25% or less.
4. The scintillator panel according to claim 1, wherein the barrier
rib has a Young's modulus of 10 GPa or more.
5. The scintillator panel according to claim 1, wherein the barrier
rib contains glass as a main component.
6. The scintillator panel according to claim 1, wherein the
scintillator panel includes a reflecting layer between the barrier
rib and the phosphor, and the reflecting layer contains a metal
oxide as a main component.
7. The scintillator panel according to claim 1, wherein the
scintillator panel includes a light shielding layer between the
barrier rib and the phosphor, and the light shielding layer
contains a metal as a main component.
8. The scintillator panel according to claim 6 or 7, wherein the
scintillator panel includes a protective layer between the
reflecting layer and the phosphor or between the light shielding
layer and the phosphor.
9. The scintillator panel according to claim 1, which is
manufactured by a method including the step of press-packing a
phosphor selected from the group consisting of CsI:Tl, NaI:Tl and
SrI2:Eu in cells separated by barrier ribs.
10. The scintillator panel according to claim 9, wherein the
pressure in the press-packing is 10 to 1000 MPa.
11. The scintillator panel according to claim 9 or 10, wherein the
temperature in the press-packing is 0 to 630.degree. C.
12. The scintillator panel according to claim 9, wherein the
press-packing is performed under vacuum.
13. The scintillator panel according to claim 9, wherein the
phosphor that is subjected to the press-packing step is in the form
of a thin-film.
14. The scintillator panel according to claim 13, wherein the
phosphor in the form of a thin-film is obtained by press-molding a
phosphor powder.
15. A radiation detector comprising the scintillator panel
according to claim 1.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
This application is the U.S. National Phase application of PCT
International Application No. PCT/JP2015/071931, filed Aug. 3,
2015, and claims priority to Japanese Patent Application No.
2014-162144, filed Aug. 8, 2014, the disclosures of each of these
applications being incorporated herein by reference in their
entireties for all purposes.
FIELD OF THE INVENTION
The present invention relates to a scintillator panel, and a
radiation detector including the scintillator panel.
BACKGROUND OF THE INVENTION
Radiation images formed using a film have been widely used
heretofore at the medical site. However, a radiation image formed
using a film presents analog image information. Thus, in recent
years, digital-type radiation detectors such as computed
radiographies (CR) and flat panel detectors (hereinafter, referred
to as "FPD") have been developed.
In the FPD, a scintillator panel is used for converting a radiation
into visible light. The scintillator panel includes a radiation
phosphor. The radiation phosphor emits visible light in response to
an applied radiation, and the emitted light is converted into an
electric signal by a TFT (thin film transistor) or a CCD
(charge-coupled device) to convert information of the radiation
into digital image information. However, the FPD has the problem
that at the time when the radiation phosphor emits light, visible
light is scattered by the radiation phosphor itself, leading to a
decrease in S/N ratio.
A method has been proposed in which for reducing influences of
scattering of emitted light, a phosphor is separated by barrier
ribs, more specifically a phosphor is packed into spaces, i.e.
cells, which are separated by preformed barrier ribs. As a method
for preforming barrier ribs, etching processing of a silicon wafer,
a screen printing method using a glass powder-containing paste, or
a photosensitive paste is known (Patent Documents 1 to 4). On the
other hand, a method is known in which a single crystal of a
phosphor is mechanically processed to form a groove, and barrier
ribs are embedded in this groove (Patent Document 5).
PATENT DOCUMENTS
Patent Document 1: Japanese Patent Laid-open Publication No.
5-60871
Patent Document 2: Japanese Patent Laid-open Publication No.
5-188148
Patent Document 3: Japanese Patent Laid-open Publication No.
2011-007552
Patent Document 4: International Publication No. WO 2012/161304
Patent Document 5: Japanese Patent Laid-open Publication No.
2004-317300
SUMMARY OF THE INVENTION
However, a method in which a phosphor is packed into cells
separated by preformed barrier ribs has the problem that scattering
of emitted light cannot be sufficiently reduced, and thus the
amount of emitted light absorbed in the barrier ribs increases,
leading to a reduction in luminance of a scintillator panel. On the
other hand, a single crystal phosphor is more desirable for
suppressing scattering of emitted light, but operations for forming
a groove in a single crystal of a phosphor are delicate, so that
not only an extremely long time is required, but also a loss occurs
in the single crystal of a phosphor due to processing, and
therefore the luminance of the scintillator panel is not sufficient
while a very high cost is required.
An object of the present invention is to provide a scintillator
panel which can be more easily and conveniently manufactured at a
low cost and which has a high luminance and a high sharpness.
The object is achieved by any of the following technical means.
(1) A scintillator panel including: a substrate; barrier ribs
placed on the substrate; and a phosphor packed into cells separated
by the barrier ribs, the phosphor being a compound selected from
the group consisting of CsI:Tl, NaI:Tl and SrI2:Eu, the phosphor
having a porosity of 20% or less and having a grain boundary.
(2) The scintillator panel according to (1), wherein the phosphor
has a porosity of 0.1% or more.
(3) The scintillator panel according to (1) or (2), wherein the
phosphor has an average particle size of 1 to 200 .mu.m.
(4) The scintillator panel according to any one of (1) to (3),
wherein the barrier rib includes an inorganic substance, and the
barrier rib has a porosity of 25% or less.
(5) The scintillator panel according to any one of (1) to (4),
wherein the barrier rib has a Young' s modulus of 10 GPa or
more.
(6) The scintillator panel according to any one of (1) to (5),
wherein the barrier rib contains glass as a main component.
(7) The scintillator panel according to any one of (1) to (6),
wherein the scintillator panel includes a reflecting layer between
the barrier rib and the phosphor, and the reflecting layer contains
a metal oxide as a main component.
(8) The scintillator panel according to any one of (1) to (7),
wherein the scintillator panel includes a light shielding layer
between the barrier rib and the phosphor, and the light shielding
layer contains a metal as a main component.
(9) The scintillator panel according to (7) or (8), wherein the
scintillator panel includes a protective layer between the
reflecting layer and the phosphor or between the light shielding
layer and the phosphor.
(10) The scintillator panel according to any one of (1) to (9),
which is manufactured by a method including the step of
press-packing a phosphor selected from the group consisting of
CsI:Tl, NaI:Tl and SrI2:Eu in cells separated by barrier ribs.
(11) The scintillator panel according to (10), wherein the pressure
in the press-packing is 10 to 1000 MPa.
(12) The scintillator panel according to (10) or (11), wherein, the
temperature in the press-packing is 0 to 630.degree. C.
(13) The scintillator panel according to any one of (10) to (12),
wherein the press-packing is performed under vacuum.
(14) The scintillator panel according to any one of (10) to (13),
wherein the phosphor that is subjected to the press-packing step is
in the form of a thin-film.
(15) The scintillator panel according to (14), wherein the phosphor
in the form of a thin-film is obtained by press-molding a phosphor
powder.
(16) A radiation detector including the scintillator panel
according to any one of (1) to (15).
According to the present invention, a scintillator panel having a
high luminance and a high sharpness can be more easily and
conveniently prepared at a low cost.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional view schematically showing a configuration of
a radiation detector including a scintillator panel according to an
embodiment of the present invention.
FIG. 2 is a perspective view schematically showing a configuration
of the scintillator panel according to an embodiment of the present
invention.
FIG. 3 is a sectional view schematically showing the configuration
of the scintillator panel according to an embodiment of the present
invention.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
Hereinafter, a specific configuration of a scintillator panel
according to embodiments of the present invention will be described
with reference to the drawings, but the present invention is not
limited thereto.
FIG. 1 is a sectional view schematically showing a configuration of
a radiation detector including the scintillator panel according to
an embodiment of the present invention. FIG. 2 is a perspective
view schematically showing a configuration of the scintillator
panel according to an embodiment of the present invention. A
radiation detector 1 includes a scintillator panel 2, an output
substrate 3 and a power supply unit 11. The scintillator panel 2
includes a phosphor layer 6, i.e. a phosphor, and the phosphor
absorbs energy of an incident radiation, and emits an
electromagnetic wave having a wavelength ranging from 300 nm to 800
nm, i.e. an electromagnetic wave (light) ranging from ultraviolet
light to infrared light with visible light at the center.
The scintillator panel 2 includes: a substrate 4; barrier ribs 5
for forming separated spaces, i.e. cells, on the substrate 4; light
shielding layers 12 formed on surfaces of the barrier ribs 5 and
areas of the substrate 4, which are not provided with the barrier
ribs; reflecting layers 13; protective layers 14; phosphor crystal
15; discontinuous boundary surface generated between crystals of
the phosphor 16; and phosphor layers 6 including a phosphor packed
into the spaces separated by the barrier ribs 5.
The output substrate 3 includes on a substrate 10 a photoelectric
conversion layer 8 and an output layer 9 in which pixels each
composed of a photoelectric conversion element and a TFT are
two-dimensionally formed. The radiation detector 1 is obtained by
bonding or adhering the light emitting surface of the scintillator
panel 2 and the photoelectric conversion layer 8 of the output
substrate 3 to each other with a barrier layer 7 interposed
therebetween, the barrier rib layer 8 being composed of a polyimide
resin etc. When light emitted from the phosphor layer 6 arrives at
the photoelectric conversion layer 8, photoelectric conversion is
performed at the photoelectric conversion layer 8, and an electric
signal is outputted through the output layer 9. In the scintillator
panel according to an embodiment of the present invention, the
cells are separated by barrier ribs, and therefore when the size
and pitch of the pixel of the photoelectric conversion element
disposed in a grid-like shape are made equal to the size and pitch
of the cell of the scintillator panel, each pixel of the
photoelectric conversion element can be associated with each cell
of the scintillator panel.
The scintillator panel according to an embodiment of the present
invention includes: a substrate; barrier ribs placed on the
substrate; and a phosphor packed into cells separated by the
barrier ribs, the phosphor having a porosity of 20% or less and
having a grain boundary.
The substrate is a flat-shaped support on which barrier ribs are
placed. The material of the substrate is, for example, a polymer, a
ceramic, a semiconductor, a metal or glass, which is permeable to a
radiation. The polymer compound is, for example, polyester,
cellulose acetate, polyamide, polyimide, polycarbonate or a carbon
fiber-reinforced resin. The ceramic is, for example, alumina,
aluminum nitride, mullite, steatite, silicon nitride or silicon
carbide. The semiconductor is, for example, silicon, germanium,
gallium arsenide, gallium phosphorus or gallium nitrogen. The metal
is, for example, aluminum, iron, copper or metal oxides. The glass
is, for example, quartz, borosilicate glass or chemically
reinforced glass.
The thickness of the substrate is preferably 1 mm or less for
suppressing absorption of a radiation by the substrate.
The reflectance of the substrate is preferably 90% or more. When
the reflectance is 90% or more, the luminance of the scintillator
panel is improved. The substrate having a reflectance of 90% or
more is, for example, a white PET film that is used as a reflecting
plate in a liquid crystal display. Here, the reflectance is a SCI
reflectance at a wavelength of 530 nm, which is measured using a
spectral colorimeter (e.g. CM-2600d; manufactured by KONICA
MINOLTA, INC.).
FIG. 3 is a sectional view schematically showing the configuration
of the scintillator panel according to an embodiment of the present
invention.
The height L1 of the barrier rib 5 is preferably 100 to 3000 .mu.m,
more preferably 160 to 1000 .mu.m. When the height L1 is more than
3000 .mu.m, light emitted by the phosphor itself may be markedly
absorbed, leading to a reduction in luminance. On the other hand,
when the height L1 is less than 100 .mu.m, the amount of the
phosphor which can be packed may decrease, leading to a reduction
in luminance of the scintillator panel.
The interval L2 between adjacent barrier ribs is preferably 30 to
1000 .mu.m. When the interval L2 is less than 30 .mu.m, it is apt
to be difficult to pack the phosphor in the cell. On the other
hand, when the interval L2 is more than 1000 .mu.m, the sharpness
of the scintillator panel may be reduced.
The bottom part width L3 of the barrier rib is preferably 5 to 150
.mu.m, more preferably 10 to 100 .mu.m. When the bottom part width
L3 is less than 5 .mu.m, so that pattern defects easily occur. On
the other hand, when the bottom part width L3 is more than 150
.mu.m, the amount of the phosphor which can be packed may decrease,
leading to a reduction in luminance of the scintillator panel.
The top part width L4 of the barrier rib is preferably 5 to 80
.mu.m. When the top part width L4 is less than 5 .mu.m, the
strength of the barrier rib is reduced, so that pattern defects
easily occur. On the other hand, when the top part width L4 is more
than 80 .mu.m, a region where light emitted by the phosphor can be
extracted may be narrowed, leading to a reduction in luminance of
the scintillator panel.
The aspect ratio (L1/L3) of the height L1 of the barrier rib to the
bottom part width L3 of the barrier rib is preferably 1.0 to 50.0.
When the aspect ratio (L1/L3) of the barrier rib increases, a space
per pixel separated by the barrier rib becomes wider, so that a
larger amount of the phosphor can be packed in the space.
The aspect ratio (L1/L2) of the height L1 of the barrier rib to the
interval L2 between barrier ribs is preferably 0.5 to 5.0, more
preferably 1.0 to 5.0. When the aspect ratio (L1/L2) of the barrier
rib increases, a pixel is finely separated, and a larger amount of
the phosphor can be packed in a space per pixel.
The height L1 of the barrier rib and the interval L2 between
adjacent barrier ribs can be measured in the following manner: a
cross-section vertical to a substrate is exposed by a polishing
apparatus such as a cross section polisher, and the cross-section
is observed with a scanning electron microscope (e.g. S2400;
manufactured by Hitachi, Ltd.). Here, L3 is the width of the
barrier rib at a contact part between the barrier rib and the
substrate. L4 is the width of the topmost part of the barrier
rib.
Preferably, the barrier rib is composed of an inorganic substance
for improving the strength and heat resistance of the barrier rib.
Here, the inorganic substance is a compound composed of some simple
carbon compound (e.g. an allotrope of carbon such as graphite or
diamond) and elements other than carbon. The term "composed of an
inorganic substance" does not exclude existence of components other
than an inorganic substance in the strict sense, and existence of
components other than an inorganic substance, such as impurities
contained in the inorganic substance serving as a raw material, and
impurities entering during manufacturing of the barrier rib, is
acceptable.
The porosity of the barrier rib is preferably 25% or less. When the
porosity is more than 25%, the strength of the barrier rib is apt
to be insufficient. The porosity of the barrier rib can be measured
in the following manner: an image of a cross-section of the barrier
rib, which is vertical to a substrate using a scanning electron
microscope, a solid portion and a void portion in the barrier rib
are distinguished from each other by binarization, and the ratio of
the void portion is determined by image analysis.
The Young's modulus of the barrier rib is preferably 10 GPa or
more. When the Young's modulus is 10 GPa or more, the strength of
the barrier rib is improved, so that the barrier rib is harder to
damage at the time of packing the phosphor. The Young's modulus of
the barrier rib can be measured by a nanoindentation method that is
a micro-region-push-in method.
Preferably, the barrier rib contains glass as a main component.
Here, the glass is an inorganic amorphous solid containing a
silicate. When the main component of the barrier rib is glass, the
strength and heat resistance of the barrier rib are improved, so
that the barrier rib is harder to rupture at the time of packing
the phosphor. The phrase "containing glass as a main component"
means that glass constitutes 50 to 100% by mass of materials for
forming the barrier rib.
In the scintillator panel according to an embodiment of the present
invention, a phosphor selected from the group consisting of CsI:Tl,
NaI:Tl and SrI2:Eu is packed in cells separated by barrier ribs.
Here, CsI:TI is cesium iodide doped with thallium as a dopant.
Similarly, NaI:Tl is sodium iodide doped with thallium as a dopant,
and SrI2:Eu is strontium iodide doped with europium as a dopant.
Preferably, the phosphor does not substantially contain an organic
substance such as a binder resin. Here, the phrase "the phosphor
does not substantially contain an organic substance" means that the
content of an organic substance in the phosphor packed in the
barrier rib is 1% by weight or less. The phosphor is composed
preferably only of a phosphor selected from the group consisting of
CsI:Tl, NaI:Tl and SrI2:Eu, but may contain other phosphor dopants
or impurities.
The porosity of the porosity of the phosphor packed in the cells
should be 20% or less, and is preferably 10% or less, more
preferably 5% or less. The porosity of the phosphor packed in the
cells is preferably 0.1% or more. When the porosity of the phosphor
is 20% or less, the packed amount of the phosphor increases, and
light scattering in the phosphor is suppressed, so that the
luminance and sharpness of the scintillator panel are improved. On
the other hand, when the porosity of phosphor is 0.1% or more, the
phosphor tends to include a proper grain boundary, so that the
luminance of the scintillator panel is easily improved. The
porosity of the packed phosphor can be measured by the same method
as that used for measuring the porosity of the barrier rib. For
minimizing a measurement error, the analyzed range of the image of
a cross-section of the phosphor, which is taken using a scanning
electron microscope, is prevented from including the barrier rib,
the substrate or the like, image analysis is performed for each of
10 randomly selected cells, the analysis results are averaged, and
the average thus obtained is defined as a porosity of the
phosphor.
The phosphor packed in the cells should have a grain boundary.
Here, the grain boundary is a discontinuous boundary surface
generated between a plurality of crystals of the phosphor. When the
phosphor packed in the cells has a grain boundary, the luminance
and sharpness of the scintillator panel is improved. Although the
mechanism thereof is not clear, it is thought that the grain
boundary serves as a waveguide because an X-ray light emission
image of a phosphor having a grain boundary shows that the grain
boundary portion particularly intensely emits light. It is thought
that due to existence of a grain boundary at a surface of the
phosphor layer, which faces the output substrate, emitted light is
easily extracted efficiently from the phosphor to the output
substrate side through the grain boundary. Presence/absence of a
grain boundary in the phosphor packed in the cell can be determined
by observing an image of a cross-section of the phosphor, which is
vertical to the substrate, using a scanning electron microscope. It
may be difficult to discriminate the outline of the grain shape
with a usual scanning microscope, but the outline of the grain
shape can be clearly discriminated by using an EBSD (electron back
scatter diffraction patterns) method.
The average particle size of the phosphor packed in the cell is
preferably 1 to 200 .mu.m. When the average particle size of the
phosphor is less than 1 .mu.m, emitted light may be excessively
scattered, leading to a reduction in luminance of the scintillator
panel. On the other hand, when the average particle size of the
phosphor is more than 200 .mu.m, the distribution of grain
boundaries and voids becomes inappropriate, leading to a reduction
in luminance of the scintillator panel. The particle size is more
preferably 10 to 100 .mu.m, still more preferably 20 to 60
.mu.m.
The average particle size of the phosphor packed in the cell is
determined in the following manner: an image of a cross-section of
the phosphor at a cross-section of the scintillator panel, which is
vertical to the substrate, is taken using a scanning electron
microscope, and for three randomly selected cells, each of
individual single crystals of the phosphor, which are separated by
grain boundaries, is regarded as one particle, and the image is
analyzed using image analysis software for all particles in the
cell. Regions separated by grain boundaries can be more clearly
observed by obtaining an image using an EBSD method as in the case
of determination of presence/absence of a grain boundary.
In the present invention, the shape of the phosphor packed in the
cell is preferably granular. An image of a cross-section of the
phosphor at a cross-section of the scintillator panel is taken
using a scanning electron microscope, and for randomly selected 10
crystals among crystals of the phosphor, which are separated grain
boundaries, the long diameter and the short diameter of the
cross-section are measured, the long diameter is divided by the
short diameter, and the values thus obtained for the 10 crystals
are averaged. When the obtained average is 10 or less, the phosphor
is granular. When the phosphor is granular, degradation of the
phosphor layer tends to more hardly occur because impurities such
as moisture are harder to enter the crystal as compared to a
nongranular phosphor such as a columnar-crystal phosphor.
Preferably, the scintillator panel according to the present
invention includes a reflecting layer, which contains a metal
oxide, between the barrier rib and the phosphor layer. Here, the
phrase "including the reflecting layer between the barrier rib and
the phosphor layer" means, for example, a state in which the
reflecting layer is formed on surfaces of the substrate and the
barrier rib, which are in contact with the phosphor layer.
Preferably, the reflecting layer contains a metal oxide as a main
component. The phrase "containing a metal oxide as a main
component" means that the ratio of a metal oxide to the reflecting
layer is 50% by volume or more. When the scintillator panel
includes the reflecting layer, which contains a metal oxide,
between the barrier rib and the phosphor layer, the reflectance of
each of the substrate and the barrier rib placed on the substrate
can be made suitable.
The average thickness of the reflecting layer is preferably 5 to 20
.mu.m. Here, the average thickness of the reflecting layer is a
value obtained by dividing the area of 10 reflecting layers, which
are randomly selected on a cross-section of the scintillator panel
vertical to the substrate, by the formation length of the
reflecting layer, and the formation length of the reflecting layer
is a total of the lengths of the portions where the reflecting
layer and the under-layer thereof (barrier rib or light shielding
etc.) are in contact with each other on the cross-sections of the
10 cells. More specifically, the average thickness of the
reflecting layer can be calculated by passing through a process in
which a cross-section of the scintillator panel vertical to the
substrate is exposed by a polishing apparatus, the cross-section is
observed with a scanning electron microscope, and image processing
is performed.
When the average thickness of the reflecting layer is less than 5
.mu.m, the reflectance may be insufficient. On the other hand, when
the average thickness of the reflecting layer is more than 20
.mu.m, the volume of the phosphor layer may be insufficient,
leading to a reduction in luminance of the scintillator panel.
The metal oxide contained in the reflecting layer is preferably a
compound selected from the group consisting of titanium oxide,
zirconium oxide and aluminum oxide for achieving a more preferred
reflectance. Preferably, the reflecting layer formed of such a
metal oxide has a suitable reflectance.
Preferably, the scintillator panel in an inspection apparatus for a
large structure according to the present invention includes the
light shielding layer, which contains a metal, between the barrier
rib and the phosphor layer. When the scintillator panel includes
the light shielding layer, which contains a metal, between the
barrier rib and the phosphor layer, leakage of scintillation light
to the adjacent cell can be inhibited. Preferably, the light
shielding layer contains a metal as a main component. The phrase
"containing a metal as a main component" means that the ratio of a
metal to the light shielding layer is 50% by volume or more.
The method for forming the light shielding layer is, for example, a
vacuum deposition method such as a vacuum vapor deposition method,
a sputtering method or a CVD method, a plating method, a paste
application method or a spraying method using a spray. The metal
contained in the light shielding layer is, for example, aluminum,
chromium, silver, tungsten, molybdenum or lead. The average
thickness of the light shielding layer is preferably 20 to 1000 nm.
When the average thickness of the light shielding layer is less
than 20 nm, the effect of suppressing leakage of scintillation
light and the effect of absorbing an X ray are apt to be
insufficient. On the other hand, when the average thickness of the
light shielding layer is more than 1000 nm, the volume of the
phosphor layer may be insufficient, leading to a reduction in
luminance of the scintillator panel. The average thickness of the
light shielding layer can be calculated by the same method as that
used for calculating the average thickness of the reflecting
layer.
When both the light shielding layer and the reflecting layer are
formed between the barrier rib and the phosphor layer, it is
preferable to form the reflecting layer on the light shielding
layer for avoiding a situation in which the reflectance becomes
insufficient due to absorption of light by the light shielding
layer.
Preferably, the protective layer is formed so that the light
shielding layer and the reflecting layer do not fall off at the
time when the phosphor is packed into the cell. When the light
shielding layer and the protective layer are formed, the protective
layer is formed between the light shielding layer and the phosphor
layer after formation of the light shielding layer. When the
reflecting layer and the protective layer are formed, the
protective layer is formed between the reflecting layer and the
phosphor layer after formation of the reflecting layer. When all of
the light shielding layer, the reflecting layer and the protective
layer are formed, it is preferable to form the light shielding
layer, the reflecting layer and the protective layer in this order.
The material of the protective layer is, for example, a substance
which is dense and strong even when being thin and which has low
reactivity, such as glass, SiO.sub.2 or resin. When a large thermal
load is applied in a post-treatment step, it is preferable to use
an inorganic substance such as glass or SiO.sub.2. On the other
hand, in the case of an organic substance, polyparaxylylene as a
resin is more preferable because it has low reactivity.
The method for forming the protective layer is, for example, a
vacuum deposition method, a plating method and a spraying method,
and a vacuum deposition method is preferable for forming a denser
film. When the thickness of the film is large, the amount of the
composition containing an inorganic material, which is packed in
cells, decreases, and therefore it is preferable that the film is
formed in the smallest thickness within such a range that the light
shielding layer and the reflecting layer do not fall off. In the
case of polyparaxylylene, it is preferable that the film is formed
in a thickness of 1 to 5 .mu.m.
Preferably, the method for manufacturing a scintillator panel
according to the present invention includes the step of
press-packing a phosphor in cells separated by barrier ribs.
The press-packing is a method in which a pressure is applied to a
phosphor to pack the phosphor in cells separated by barrier ribs. A
phosphor selected from the group consisting of CsI:Tl, NaI:Tl and
SrI2:Eu can be packed into barrier ribs uniformly and with a low
porosity even under mild conditions of a relatively low temperature
and low pressure because the phosphor has such a unique nature that
crystals are plastically even at a low temperature and low
pressure. On the other hand, other phosphors are very difficult to
press-pack because they have the problem that the phosphor is not
plastically deformed, and thus the porosity of the phosphor layer
after packing of the phosphor into the barrier rib cannot be
reduced to 20% or less, that the phosphor itself is degraded under
pressure, that a high temperature and high pressure is required for
high-density packing, and therefore deformation or rupture of
barrier ribs cannot be avoided, and so on.
The method for applying a pressure to the phosphor is, for example,
uniaxial pressing, cold isostatic pressing or hot isostatic
pressing.
The pressure in press-packing is preferably 10 to 1000 MPa, more
preferably 50 to 400 MPa. When the pressure in press-packing is
less than 10 MPa, plastic deformation of the phosphor may be so
insufficient that the porosity does not decrease, and thus emitted
light is excessively scattered, leading to a reduction in luminance
of the scintillator panel. On the other hand, when the pressure in
press-packing is more than 1000 MPa, the phosphor may be
single-crystallized, leading to a reduction in luminance of the
scintillator panel, and deformation or rupture of barrier ribs
easily occurs.
The temperature in press-packing is preferably 0 to 630.degree. C.
When the temperature in press-packing is higher than 630.degree.
C., the phosphor may be single-crystallized, leading to a reduction
in luminance of the scintillator panel, and deformation or rupture
of barrier ribs easily occurs. The temperature in press-packing is
more preferably 500.degree. C. or lower, still more preferably
300.degree. C. or lower.
Preferably, press-packing is performed under vacuum. When
press-packing is performed under vacuum, the porosity of the
phosphor layer is easily reduced. The method for performing packing
under vacuum is not particularly limited, and may be a method in
which pressing is performed while a pressing mechanism unit of a
press machine is kept under vacuum, or a method in which an object
to be pressed is put in a plastic bag or a metal thin-film
container sealed and molded in the form of a bag, the inside of the
bag is then evacuated into vacuum, and the bag is then pressed.
Methods for applying a pressure to an object in the form of a bag
are classified into several methods according to a medium to be
used, a heating temperature, or the like, and examples thereof
include a CIP method, a WIP method and a HIP method. Here, the CIP
method (cold isostatic pressing method) is a method in which a
liquid such as water is used as a medium, and heating is not
performed; the WIP method (warm isostatic pressing method) is a
method in which a liquid such as water or silicon oil is used as a
medium, and heating is performed at 15 to 200.degree. C.; and the
HIP method (hot isostatic pressing method) is a method in which an
argon gas or nitrogen gas is used as a medium, and heating is
performed at 15 to 2500.degree. C.
The phosphor to be press-packed is preferably in the form of a
powder or thin film (sheet), more preferably in the form of a thin
film. The method for obtaining a phosphor in the form of a thin
film is preferably a method in which a powdered phosphor is
press-molded. When the phosphor is formed into a thin film, then
disposed on the opening surfaces of cells, and press-packed, the
porosity of the phosphor layer can be further reduced.
After the phosphor is packed, an excess composition may be wiped
off with a solvent etc., or mechanically abraded. When the
thickness of the excess phosphor is large, emitted light is easily
scattered in the horizontal direction of the display member.
Therefore, it is preferable that the thickness of the composition
is adjusted during packing so that the height of the packed
composition is equivalent to the height of the barrier rib, or the
excess composition is wiped off with a solvent etc. after packing,
or removed by abrading after packing.
As a method for forming the barrier rib, a known method can be
used, but a photosensitive paste method is preferable because shape
control is easy.
For example, barrier ribs containing glass as a main component can
be formed through an application step of applying a photosensitive
paste, contains a glass powder, to a surface of a base material to
obtain an applied film; a pattern forming step of exposing and
developing the applied film to obtain a pre-firing pattern of the
barrier rib; and a firing step of firing a pattern to obtain a
barrier rib pattern. For manufacturing barrier ribs containing
glass as a main component, a glass powder should constitute 50 to
100% by mass of inorganic components contained in the glass
powder-containing paste that is used in the application step.
The glass powder contained in the glass powder-containing paste is
preferably a powder of glass that is softened at a firing
temperature, more preferably a powder of low-softening-point glass
having a softening temperature of 700.degree. C. or lower.
The softening temperature can be determined by extrapolating a heat
absorption end temperature at an endothermic peak by a tangent
method from a DTA curve obtained by measuring a sample using a
differential thermal analyzer (e.g. Differential thermogravimetric
analyzer TG8120; manufactured by Rigaku Corporation). More
specifically, first an inorganic powder as a measurement sample is
measured with the temperature elevated at a rate of 20.degree.
C./minute from room temperature using a differential thermal
analyzer, so that a DTA curve is obtained. In this measurement, an
alumina powder is used as a standard sample. From the obtained DTA
curve, a softening point Ts is determined by extrapolating a heat
absorption end temperature at an endothermic peak by a tangent
method. The softening point Ts can be defined as a softening
temperature.
For obtaining low-softening-point glass, a metal oxide selected
from the group consisting of lead oxide, bismuth oxide, zinc oxide
and an oxide of an alkali metal, each of which is a compound
effective for lowering the softening point of glass, can be used,
but it is preferable to adjust the softening temperature of glass
using an oxide of an alkali metal. Here, the alkali metal is a
metal selected from the group consisting of lithium, sodium and
potassium.
The ratio of the alkali metal oxide to the low-softening-point
glass is preferably 2 to 20% by mass. When the ratio of the alkali
metal oxide is less than 2% by mass, the softening temperature
increases, and thus it is necessary to carry out the firing step at
a high temperature, so that defects easily occur in barrier ribs.
On the other hand, when the ratio of the alkali metal oxide is more
than 20% by mass, the viscosity of glass excessively decreases in
the firing step, so that the shape of the resulting grid-like
post-firing pattern is easily strained.
Preferably, the low-softening-point glass contains 3 to 10% by mass
of zinc oxide for the glass to have an optimum viscosity at a high
temperature. When the ratio of zinc oxide to the
low-softening-point glass is less than 3% by mass, the viscosity at
a high temperature increases. On the other hand, when the content
of zinc oxide is more than 10% by mass, the manufacturing cost of
the low-softening-point glass increases.
Preferably, the low-softening-point glass contains a metal oxide
selected from the group consisting of silicon oxide, boron oxide,
aluminum oxide and an oxide of an alkali earth metal for adjusting
stability, crystallinity, transparency, a refractive index or
thermal expansion characteristics. Here, the alkali earth metal is
a metal selected from the group consisting of magnesium, potassium,
barium and strontium. One example of the composition range for
preferred low-softening-point glass is shown below. Alkali metal
oxide: 2 to 20% by mass Zinc oxide: 3 to 10% by mass Silicon oxide:
20 to 40% by mass Boron oxide: 25 to 40% by mass Aluminum oxide: 10
to 30% by mass Alkali earth metal oxide: 5 to 15% by mass
The particle size of an inorganic powder including a glass powder
can be measured using a particle size distribution analyzer (e.g.
MT3300; manufactured by NIKKISO Co., Ltd.). More specifically, an
inorganic powder is added in a water-filled sample chamber of a
particle size distribution analyzer, and subjected to an ultrasonic
treatment for 300 seconds, and the particle size of the inorganic
powder is then measured.
The 50%-volume average particle size (hereinafter, referred to as
"D50") of the low-softening-point glass powder is preferably 1.0 to
4.0 .mu.m. When the volume average particle size D50 is less than
1.0 .mu.m, the glass powder is aggregated, and thus uniform
dispersibility is no longer obtained, so that flow stability of the
paste is deteriorated. On the other hand, when the volume average
particle size D50 is more than 4.0 .mu.m, the surface irregularity
of a post-firing pattern obtained in the firing step becomes
larger, so that the barrier rib may be easily ruptured later.
The glass powder-containing paste may contain, in addition to
low-softening-point glass, high-softening-point, glass having a
softening temperature of 700.degree. C. or higher, or ceramic
particles such as those of silicon oxide, aluminum oxide, titanium
oxide or zirconium oxide as a filler for control of the shrinkage
ratio of a grid-like pattern in the firing step, and retention of
the shape of the barrier rib that is finally obtained. The ratio of
the filler to all the inorganic components is preferably 50% by
mass or less for preventing a reduction in strength of the barrier
rib due to hindrance of sintering of the glass powder. The volume
average particle size D50 of the filler is preferably the same as
that of the low-softening-point glass powder.
In a photosensitive glass powder-containing paste, the refractive
index n1 of the glass powder and the refractive index n2 of the
organic component satisfy the relationship of preferably
-0.1<n1-n2<0.1, more preferably
-0.01.ltoreq.n1-n2.ltoreq.0.01, still more preferably
-0.005.ltoreq.n1-n2.ltoreq.0.005 for suppressing light scattering
during exposure to form a precise pattern. The refractive index of
the glass powder can be appropriately adjusted according to the
composition of a metal oxide contained in the glass powder.
The refractive index of the glass powder can be measured by a Becke
line detection method. The refractive index of the organic
component can be determined by measuring a coating film composed of
the organic component by ellipsometry. More specifically, the
refractive index (ng) to light having a wavelength of 436 nm
(g-ray) at 25.degree. C. can be defined as n1 for the glass powder
and n2 for the organic component.
The photosensitive organic component contained in the
photosensitive glass powder-containing paste is, for example, a
photosensitive monomer, a photosensitive oligomer or a
photosensitive polymer. Here, the photosensitive monomer,
photosensitive oligomer or photosensitive polymer is a monomer,
oligomer of polymer which causes a reaction such as
photo-crosslinking or photo-polymerization to change its chemical
structure when irradiated with active light.
The photosensitive monomer is preferably a compound having an
active carbon-carbon unsaturated double bond. The compound is, for
example, a compound having a vinyl group, an acryloyl group, a
methacryloyl group or an acrylamide group, and a polyfunctional
acrylate compound or a polyfunctional methacrylate compound is
preferable for increasing the density of photo-crosslinking to form
a precise pattern.
The photosensitive oligomer or photosensitive polymer is an
oligomer or polymer having an active carbon-carbon unsaturated
double bond and having a carboxyl group. The oligomer or polymer is
obtained by, for example, a carboxyl group-containing monomer such
as acrylic acid, methacrylic acid, itaconic acid, crotonic acid,
maleic acid, fumaric acid, vinyl acetic acid or an acid anhydride
thereof, a methacrylic acid ester, an acrylic acid ester, styrene,
acrylonitrile, vinyl acetate or 2-hydroxy acrylate. The method for
introducing an active carbon-carbon unsaturated double bond into an
oligomer or polymer is, for example, a method in which chloride
acrylate, chloride methacrylate, allyl chloride, an ethylenically
unsaturated compound having a glycidyl group or an isocyanate
group, or a carboxylic acid such as maleic acid is reacted with a
mercapto group, an amino group, a hydroxyl group or a carboxyl
group in the oligomer or polymer.
By using a photosensitive monomer or photosensitive oligomer having
a urethane bond, a glass powder-containing paste which is capable
of relaxing stress in the initial stage of the firing step and
which hardly causes damage to a pattern in the firing step.
The photosensitive glass powder-containing paste may contain a
photo-polymerization initiator as necessary. Here, the
photo-polymerization initiator is a compound which generates a
radical when irradiated with active light. The photo-polymerization
initiator is, for example, benzophenon, methyl o-benzoylbenzoate,
4,4-bis(dimethylamino)benzophenone,
4,4-bis(diethylamino)benzophenone, 4,4-dichlorobenzophenone,
4-benzoyl-4-methyldiphenylketone, dibenzylketone, fluorenone,
2,2-dimethoxy-2-phenylacetophenone,
2-hydroxy-2-methylpropiophenone, thioxanthone,
2-methylthioxanthone, 2-chlorothioxanthone,
2-isopropylthioxanthone, diethylthioxanthone, benzyl, benzyl
methoxyethyl acetal, benzoin, benzoin methyl ether, benzoin butyl
ether, anthraquinone, 2-t-butylanthraquinone, anthrone,
benzanthrone, dibenzosuberone, methylene anthrone,
4-azidebenzalacetophenone,
2,6-bis(p-azidebenzylidene)cyclohexanone,
2,6-bis(p-azidebenzylidene)-4-methylcyclohexanone,
1-phenyl-1,2-butadione-2-(O-methoxycarbonyl)oxime,
1-phenyl-1,2-propanedione-2-(O-ethoxycarbonyl)oxime,
1,3-diphenylpropanetrione-2-(O-ethoxycarbonyl)oxime,
1-phenyl-3-ethoxypropanetrione-2-(O-benzoyl)oxime, Michler's
ketone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-1-propanone,
2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone-1,
naphthalenesulfonyl chloride, N-phenylthioacridone, benzthiazole
disulfide, triphenylwholphin, or a combination of a photo-reducing
dye such as eosine or methylene blue and a reducing agent such as
ascorbic acid or triethanolamine.
When the photosensitive glass powder-containing paste contains a
polymer having a carboxyl group as a photosensitive polymer,
solubility in an alkali aqueous solution during development is
improved. The acid value of the polymer having a carboxyl group is
preferably 50 to 150 mg KOH/g. When the acid value is 150 mg KOH/g
or less, the development margin is widened. On the other hand, when
the acid value is 50 mg KOH/g or more, solubility in an alkali
aqueous solution is not reduced, and a fine pattern can be
obtained.
The photosensitive glass powder-containing paste can be obtained by
blending various kinds of components so as to achieve a
predetermined composition, and then homogeneously mixing and
dispersing the blend by three rollers or a kneader.
The viscosity of the photosensitive glass powder-containing paste
can be appropriately adjusted according to the addition ratio of an
inorganic powder, a thickener, an organic solvent, a polymerization
inhibitor, a plasticizer, a precipitation preventive agent or the
like, but it is preferably in the range of 2 to 200 Pas. For
example, the viscosity is preferably 2 to 5 Pas when the
photosensitive glass powder-containing paste is applied to a base
material by a spin coating method, and the viscosity is preferably
10 to 50 Pas when the photosensitive glass powder-containing paste
is applied to a base material by a blade coater method or a die
coater method. When the photosensitive glass powder-containing
paste is applied by a screen printing method once to obtain an
applied film having a thickness of 10 to 20 .mu.m, the viscosity is
preferably 50 to 200 Pas.
The application step is a step of applying the glass
powder-containing paste to the whole or a part of a surface of a
base material to obtain an applied film. As the base material, a
support having high heat resistance, such as a glass plate or a
ceramic plate, can be used. The method for applying the glass
powder-containing paste is, for example, a screen printing method,
a bar coater, a roll coater, a die coater or a blade coater. The
thickness of the resulting applied film can be adjusted according
to the number of times of application, the mesh size of a screen,
the viscosity of the paste, or the like.
The pattern forming step may include, for example, an exposure step
of exposing the applied film obtained in the application step,
through a photomask having a predetermined opening, and a
development step of dissolving and removing a portion of the
post-exposure applied film, which is soluble in a developer.
The exposure step is a step of photo-curing a necessary portion of
the applied film by exposure or photo-decomposing an unnecessary
portion of the applied film, so that an arbitrary portion of the
applied film is soluble in a developer. The development step is a
step of dissolving and removing a portion of the post-exposure
applied film, which is soluble in a developer, with the developer
to obtain a grid-like pre-firing pattern in which only a necessary
portion remains.
In the exposure step, an arbitrary pattern may be directly drawn
with laser light etc. without using a photomask. The exposure
apparatus is, for example, a proximity exposure machine. The active
light to be applied in the exposure step is, for example, near
infrared light, visible light or ultraviolet light, and ultraviolet
light is preferable. The light source is, for example, a
low-pressure mercury lamp, a high-pressure mercury lamp, an
ultra-high-pressure mercury lamp, a halogen lamp or a bactericidal
lamp, and an ultra-high-pressure mercury lamp is preferable.
Exposure conditions vary depending on the thickness of the applied
film, but commonly the applied film is exposed for 0.01 to 30
minutes using an ultra-high-pressure mercury lamp with an output of
1 to 100 mW/cm.sup.2.
The method for development in the development step is, for example,
an immersion method, a spray method or a brush method. As the
developer, a solvent capable of dissolving an unnecessary portion
of the post-exposure applied film may be appropriately selected,
but an aqueous solution containing water as a main component is
preferable. For example, when the glass powder-containing paste
contains a polymer having a carboxyl group, an alkali aqueous
solution can be selected as the developer. The alkali aqueous
solution is, for example, an inorganic alkali aqueous solution such
as that of sodium hydroxide, sodium carbonate or potassium
hydroxide, or an organic alkali aqueous solution such as that of
tetramethylammonium hydroxide, trimethylbenzylammonium hydroxide or
diethanolamine, and an organic alkali aqueous solution is
preferable because it is easily removed in the firing step. The
concentration of the alkali aqueous solution is preferably 0.05 to
5% by mass, more preferably 0.1 to 1% by mass. When the alkali
concentration is less than 0.05% by mass, it may be unable to
sufficiently remove an unnecessary portion of the post-exposure
applied film. On the other hand, when the alkali concentration is
more than 5% by mass, the grid-like pre-firing pattern may be
peeled or corroded. The development temperature is preferably 20 to
50.degree. C. for facilitating process control.
For forming a pattern by exposure and development, the glass
powder-containing paste to be applied in the application step
should be photosensitive. In other words, the glass
powder-containing paste should contain a photosensitive organic
component. The ratio of the organic component to the photosensitive
glass powder-containing paste is preferably 30 to 80% by mass, more
preferably 40 to 70% by mass. When the ratio of the organic
component is less than 30% by mass, not only dispersibility of the
inorganic component in the paste is deteriorated, so that defect
easily occur in the firing step, but also the viscosity of the
paste increases, so that coatability is deteriorated, and further
stability of the paste is easily deteriorated. On the other hand,
when the ratio of the organic component is more than 80% by mass,
the shrinkage ratio of the grid-like pattern in the firing step
increases, so that defects easily occur.
Preferably, the glass powder contained in the photosensitive glass
powder-containing paste has a softening temperature of 480.degree.
C. or higher for almost completely removing the organic component
in the firing step to secure the strength of the barrier rib that
is finally obtained. When the softening temperature is lower than
480.degree. C., there is the possibility that the glass powder is
softened before the organic component is sufficiently removed in
the firing step, so that the organic component remains in glass
after sintering, and induces coloring of the barrier rib, leading
to a reduction in luminance of the scintillator panel.
The firing step is a step of firing the grid-like pre-firing
pattern, which is obtained in the pattern forming step, to dissolve
and remove the organic component contained in the glass
powder-containing paste, and softening and sintering the glass
powder to obtain a grid-like post-firing pattern, i.e. the barrier
rib. Firing conditions vary depending on the composition of the
glass powder-containing paste and the type of the base material,
and firing can be performed in a firing furnace in an atmosphere
of, for example, air, nitrogen or hydrogen. The firing furnace is,
for example, a batch-type firing furnace or a belt-type continuous
firing furnace. The temperature of firing is preferably 500 to
1000.degree. C., more preferably 500 to 800.degree. C., still more
preferably 500 to 700.degree. C. When the firing temperature is
lower than 500.degree. C., the organic component is not
sufficiently decomposed and removed. On the other hand, the firing
temperature is higher than 1000.degree. C., the base material that
can be used is limited to a ceramic plate etc. having high heat
resistance. The firing time is preferably 10 to 60 minutes.
An article obtained by packing a phosphor in cells separated by
barrier ribs as described above may be used as a scintillator panel
(here, the base material used serves as a substrate in the
scintillator panel according to the present invention), or barrier
ribs and a phosphor may be separated from a base material after
press-packing, and placed on a separately provided substrate to
complete a scintillator panel.
EXAMPLES
The present invention will be described further in detail below by
way of examples and comparative examples, but the present invention
is not limited to these examples.
(Method for Measuring Porosity)
A scintillator panel was cut in a direction vertical to a
substrate, the cut surface was then abraded by an ion milling
method to expose a cross-section vertical to the substrate, and an
electrical conductivity imparting treatment (Pt coating) was
performed to prepare a measurement sample. Thereafter, a
cross-section image was obtained using a field
emission.quadrature.type scanning electron microscope S-4800
(manufactured by Hitachi High-Technologies Corporation.). For the
obtained image, a solid portion and a void portion were
distinguished from each other by binarization, and the ratio of the
void portion was determined by image analysis to measure the
porosity. For minimizing a measurement error, the analyzed range of
the image of a cross-section of the phosphor was prevented from
including the barrier rib, the substrate or the like, image
analysis was performed for each of 10 randomly selected cells, the
analysis results were averaged, and the average thus obtained was
defined as a porosity of the phosphor.
(Method for Determining Presence/Absence of Grain Boundary and
Method for Measuring Average Particle Size)
A measurement sample was prepared in the same manner as in
measurement of the porosity. Thereafter, a cross-section crystal
orientation image was obtained by an EBSD method using JSM-6500F
(manufactured by JEOL Ltd.) equipped with a DVC-type EBSD
(manufactured by TSL Company). Using attached software, the
obtained image was analyzed for three randomly selected cells to
detect a crystal grain boundary of a phosphor as a closed boundary
having an angle of 5 degrees or more, and it was determined that a
grain boundary was present when a grain boundary was detected in
the phosphor for each of the cells. The average particle size was
calculated in terms of an area average particle size for crystal
grains in the three cells using attached software. When a grain
boundary was not present in the phosphor, the phosphor included in
one cell was regarded as one particle, and the average particle
size was calculated.
(Phosphor)
As powders of CsI:Tl, NaI:Tl and SrI2:Eu, those obtained by
grinding commercially available phosphor single crystals in dry
air, and causing the resulting particles to pass through a sieve to
remove coarse particles. As GOS:Tb (gadolinium oxysulfide doped
with Tb), a commercial product was used as it was.
(Raw Material of Glass Powder-Containing Paste)
Raw materials used for preparation of a photosensitive glass
powder-containing paste are as follows. Photosensitive monomer M-1:
trimethylolpropane triacrylate Photosensitive monomer M-2:
tetrapropylene glycol dimethacrylate Photosensitive polymer:polymer
obtained by addition reaction of 0.4 equivalents of glycidyl
methacrylate with a carboxyl group of copolymer of methacrylic
acid/methyl methacrylate/styrene at a mass ratio of 40:40:30 (mass
average molecular weight: 43000; acid value: 100).
Photo-polymerization initiator:
2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butano ne-1(IC369;
manufactured by BASF SE). Polymerization inhibitor:
1,6-hexanediol-bis[(3,5-di-t-butyl-4-hydroxyphenyl)propionate]).
Ultraviolet ray absorber solution: 0.3 mass % .gamma.-butyrolactone
solution of Sudan IV (manufactured by TOKYO OHKA KOGYO Co., Ltd.).
Viscosity modifier: FLOWNON EC121 (manufactured by KYOEISHA
CHEMICAL Co., LTD). Solvent: .gamma.-butyrolactone.
Low-softening-point glass powder: SiO.sub.2: 27% by mass,
B.sub.2O.sub.3: 31% by mass, ZnO: 6% by mass, Li.sub.2O: 7% by
mass, MgO: 2% by mass, CaO: 2% by mass, BaO: 2% by mass,
Al.sub.2O.sub.3: 23% by mass, refractive index (ng): 1.56, glass
softening temperature; 588.degree. C., thermal expansion
coefficient: 70.times.10.sup.-7 (K.sup.-1), average particle size:
2.3 .mu.m. High-softening-point glass powder: SiO.sub.2: 30% by
mass, B.sub.2O.sub.3: 31% by mass, ZnO: 6% by mass, MgO: 2% by
mass, CaO: 2% by mass, BaO: 2% by mass, Al.sub.2O.sub.3: 27% by
mass, refractive index (ng): 1.55, softening temperature;
790.degree. C., thermal expansion coefficient: 32.times.10.sup.-7
(K.sup.-1), average particle size: 2.3 .mu.m.
(Preparation of Glass Powder-containing Paste)
4 parts by mass of a photosensitive monomer M-1, 6 parts by mass of
a photosensitive monomer M-2, 24 parts by mass of a photosensitive
polymer, 6 parts by mass of a photo-polymerization initiator, 0.2
parts by mass of a polymerization inhibitor and 12.8 parts by mass
of an ultraviolet ray absorber solution were heated and dissolved
in 38 parts by mass of a solvent at a temperature of 80.degree. C.
The obtained solution was cooled, and 9 parts by mass of a
viscosity modifier was then added to obtain an organic solution 1.
The obtained organic solution 1 was applied to a glass plate, and
dried to obtain an organic coating film. The organic coating film
had a refractive index (ng) of 1.555.
To 50 parts by mass of the organic solution 1 were added 40 parts
by mass of a low-softening-point glass powder and 10 parts by mass
of a high-softening-point glass powder, and the mixture was then
kneaded by a three roll mill to obtain a glass powder-containing
paste.
(Raw Materials of Reflecting Layer Paste)
Raw materials used for preparation of a reflecting layer paste are
as follows. Filler: titanium oxide (manufactured by Ishihara Sangyo
Kaisha, Ltd.). Binder solution: mixed solution of 5% by mass of
ethyl cellulose (manufactured by The Dow Chemical Company) and 95%
by mass of terpineol (Nippon Terpene Chemicals, Inc.). Monomer:
mixture of 30% by mass of dipentaerythritol pentaacrylate and 70%
by mass of dipentaerythritol hexaacrylate (each manufactured by
Toagosei Company, Limited). Polymerization initiator:
1,1'-azobis(cyclohexane-1-carbonitrile) (V-40; manufactured by Wako
Pure Chemical Industries, Ltd.).
(Preparation of Reflecting Layer Paste)
50 parts by mass of a filler, 45 parts by mass of a binder
solution, 4.5 parts by mass of a monomer and 1.5 parts by mass of a
polymerization initiator were kneaded by a three roll mill to
obtain a reflecting layer paste.
(Formation of Barrier Rib)
A soda glass plate having a size of 125 mm.times.125 mm.times.0.7
mm was used as a base material. The glass powder-containing paste
was applied to a surface of the base material by a die coater so as
to achieve a thickness of 500 .mu.m after drying, and dried to
obtain a glass powder-containing paste applied film. Next, using an
ultra-high-pressure, the glass powder-containing paste applied film
was exposed with an exposure amount of 500 mJ/cm.sup.2 through a
photomask (chromium mask having a pitch of 194 .mu.m and a line
width of 20 .mu.m and having a grid-like opening), the photomask
having an opening corresponding to a desired pattern. The applied
film after exposure was developed in a 0.5 mass % ethanol amine
aqueous solution, so that unexposed portion was removed to obtain a
grid-like pre-firing pattern. The obtained grid-like pre-firing
pattern was fired at 585.degree. C. for 15 minutes in air to form
grid-like barrier ribs containing glass as a main component. The
porosity of the barrier rib was 2.5%, the height L1 of the barrier
rib was 350 .mu.m, the interval L2 between barrier ribs was 194
.mu.m, the bottom part width L3 of the barrier rib was 35 .mu.m,
and the top part width L4 of the barrier rib was 20 .mu.m, and the
Young's modulus of the barrier rib was 20 GPa.
Example 1
0.11 g/cm.sup.2 of a CsI:Tl powder was supplied onto a base
material provided with grid-like barrier ribs, and was flattened by
a squeegee, and put in a Nylon (registered trademark) bag together
with the base material, and the opening of the bag was thermally
welded to seal the bag. The bag was set in an isostatic pressure
press apparatus (manufactured by Kobe Steel, Ltd.), and the powder
was press-packed at a pressure of 400 MPa and a temperature of
25.degree. C. to prepare a scintillator panel 1.
The CsI:TI packed in cells had a grain boundary. The CsI:TI packed
in the cells had a porosity of 5% and an average particle size of
25 .mu.m.
The prepared scintillator panel 1 was set in a FPD (PaxScan3030;
manufactured by Varian Company) to prepare a radiation detector.
The radiation detector was irradiated with an X-ray with a tube
voltage of 60 kVp from the substrate side of the scintillator panel
1, and the amount of light emitted from a scintillator layer was
detected by the FPD to evaluate the luminance of the scintillator
panel 1. The image sharpness of the scintillator panel 1 was
evaluated on the basis of a photographed image of a short wave
chart. The scintillator panel 1 exhibited a good luminance and
image sharpness.
Example 2
Except that in press-packing, the pressure was 60 MPa, and the
temperature was 150.degree. C., the same procedure as in Example 1
was carried out to prepare a scintillator panel, and evaluation was
performed. The phosphor packed in cells of the obtained
scintillator panel 2 had a grain boundary, and had a porosity of 2%
and an average particle size of 35 .mu.m. The luminance of the
scintillator panel 2 was 110 in terms of a relative value where the
luminance of the scintillator panel 1 is 100. Thus, the
scintillator panel 2 exhibited a good luminance. The scintillator
panel 2 also exhibited a good image sharpness.
Example 3
The reflecting layer paste was applied to a surface of a base
material provided with grid-like barrier ribs, and was left
standing for 5 minutes, and the deposited reflecting layer paste
was then scraped off by a rubber squeegee with a hardness of
80.degree.. Thereafter, drying was performed in hot air ovens at
80.degree. C..degree. and 130.degree. C. for 30 minutes each to
form a reflecting layer on the surface of the barrier rib and on
portions where the barrier rib was not formed. Thereafter, in the
same manner as in Example 1, a CsI:Tl powder was supplied, and
press-packed to prepare a scintillator panel 3, and evaluation was
performed.
The phosphor packed in cells of the obtained scintillator panel 3
had a grain boundary, and had a porosity of 5% and an average
particle size of 25 .mu.m. The luminance of the scintillator panel
2 was 130 in terms of a relative value where the luminance of the
scintillator panel 1 is 100. Thus, the scintillator panel 2
exhibited a good luminance. The scintillator panel 3 also exhibited
a good image sharpness.
Example 4
In the same manner as in Example 3, a reflecting layer was formed
on a surface of a base material provided with grid-like barrier
ribs. Thereafter, 0.11 g/cm.sup.2 of a CsI:Tl powder was supplied
onto the base material, flattened by a squeegee, and put in a Nylon
(registered trademark) bag together with the base material. Next,
using a vacuum packaging machine (TOSPACK V-280; manufactured by
TOSEI CORPORATION), the bag was evacuated for 30 seconds, and then
thermally welded to be sealed. Thereafter, the same procedure as in
Example 3 was carried out to prepare a scintillator panel 4, and
evaluation was performed.
The phosphor packed in cells of the obtained scintillator panel 4
had a grain boundary, and had a porosity of 4% and an average
particle size of 30 .mu.m. The luminance of the scintillator panel
6 was 135 in terms of a relative value where the luminance of the
scintillator panel 1 is 100. Thus, the scintillator panel 6
exhibited a good luminance. The scintillator panel 4 also exhibited
a good image sharpness.
Example 5
A rubber sheet having a thickness of about 1 mm was bored by a size
larger than a packing area to form a rubber frame, the rubber frame
was placed on a SUS plate, and 0.11 g/cm.sup.2 of a CsI:Tl powder
was supplied, and leveled. Thereafter, the SUS plate, the rubber
frame and the CsI:TI powder were put in a Nylon (registered
trademark) bag. Next, using a vacuum packaging machine (TOSPACK
V-280; manufactured by TOSEI CORPORATION), the bag was evacuated
for 30 seconds, and then thermally welded to be sealed. The bag was
set in an isostatic pressure press apparatus (manufactured by Kobe
Steel, Ltd.), and pressed at a pressure of 400 MPa and a
temperature of 25.degree. C. to prepare a CsI:Tl press-molded film
1.
In the same manner as in Example 3, a reflecting layer was formed
on a surface of a base material provided with grid-like barrier
ribs. Thereafter, the press-molded film 1 was supplied onto the
base material, and put in a Nylon (registered trademark) bag
together with the base material. Next, using a vacuum packaging
machine (TOSPACK V-280; manufactured by TOSEI CORPORATION), the bag
was evacuated for 30 seconds, and then thermally welded to be
sealed. Thereafter, in the same manner as in Example 3,
press-packing was performed to prepare a scintillator panel 5, and
evaluation was performed.
The phosphor packed in cells of the obtained scintillator panel 5
had a grain boundary, and had a porosity of 3% and an average
particle size of 30 .mu.m. The luminance of the scintillator panel
6 was 140 in terms of a relative value where the luminance of the
scintillator panel 1 is 100. Thus, the scintillator panel 6
exhibited a good luminance. The scintillator panel 5 also exhibited
a good image sharpness.
Example 6
On a surface of a base material provided with grid-like barrier
ribs, an aluminum film was formed in a thickness of 0.4 .mu.m by a
sputtering method to form a light shielding layer. Thereafter, in
the same manner as in Example 5, the press-molded film 1 was
press-packed to prepare a scintillator panel 6, and evaluation was
performed.
The phosphor packed in cells of the obtained scintillator panel 6
had a grain boundary, and had a porosity of 3% and an average
particle size of 30 .mu.m. The luminance of the scintillator panel
6 was 80 in terms of a relative value where the luminance of the
scintillator panel 1 is 100. Thus, the scintillator panel 6
exhibited a relatively good luminance. The scintillator panel 6
exhibited an extremely good image sharpness.
Example 7
In the same manner as in Example 3, a reflecting layer was formed
on a surface of a base material provided with grid-like barrier
ribs. On the base material after formation of the reflecting layer,
a polyparaxylylene film was formed in a thickness of 4 .mu.m by
vapor deposition polymerization to form a protective layer.
Thereafter, in the same manner as in Example 5, the press-molded
film 1 was press-packed to prepare a scintillator panel 7, and
evaluation was performed.
The phosphor packed in cells of the obtained scintillator panel 7
had a grain boundary, and had a porosity of 3% and an average
particle size of 30 .mu.m. The luminance of the scintillator panel
7 was 150 in terms of a relative value where the luminance of the
scintillator panel 1 is 100. Thus, the scintillator panel 7
exhibited a good luminance. The scintillator panel 7 also exhibited
a good image sharpness.
Example 8
In the same manner as in Example 6, a light shielding layer was
formed on a surface of a base material provided with grid-like
barrier ribs. Next, in the same manner as in Example 3, a
reflecting layer was formed on the base material provided with the
light shielding layer. Further, in the same manner as in Example 7,
a protective layer was formed on the base material provided with
the light shielding layer and the reflecting layer. Thereafter, in
the same manner as in Example 5, the press-molded film 1 was
press-packed to prepare a scintillator panel 8, and evaluation was
performed.
The phosphor packed in cells of the obtained scintillator panel 8
had a grain boundary, and had a porosity of 3% and an average
particle size of 30 .mu.m. The luminance of the scintillator panel
8 was 130 in terms of a relative value where the luminance of the
scintillator panel 1 is 100. Thus, the scintillator panel 8
exhibited a good luminance. The scintillator panel 6 exhibited an
extremely good image sharpness.
Example 9
Except that in press-packing, the pressure was 200 MPa, and the
temperature was 150.degree. C., the same procedure as in Example 5
was carried out to prepare a scintillator panel 9, and evaluation
was performed.
The phosphor packed in cells of the obtained scintillator panel 9
had a grain boundary, and had a porosity of 0.6% and an average
particle size of 45 .mu.m. The luminance of the scintillator panel
9 was 150 in terms of a relative value where the luminance of the
scintillator panel 1 is 100. Thus, the scintillator panel 9
exhibited a good luminance. The scintillator panel 9 also exhibited
a good image sharpness.
Example 10
Except that the medium was changed to metal foil capsule having a
thickness of 100 .mu.m (sealed by a metal foil capsule sealing
apparatus (Kobe Steel, Ltd.) as a packaging bag used in
press-packing, the press pressure was 400 MPa, and the temperature
was 300.degree. C., the same procedure as in Example 5 was carried
out to prepare a scintillator panel 10, and evaluation was
performed.
The phosphor packed in cells of the obtained scintillator panel 10
had a grain boundary, and had a porosity of 0.2% and an average
particle size of 50 .mu.m. The luminance of the scintillator panel
10 was 150 in terms of a relative value where the luminance of the
scintillator panel 1 is 100. Thus, the scintillator panel 10
exhibited a good luminance. The scintillator panel 10 also
exhibited a good image sharpness.
Example 11
Except that in press-packing, the pressure was 400 MPa, and the
temperature was 550.degree. C., the same procedure as in Example 10
was carried out to prepare a scintillator panel 11, and evaluation
was performed.
The phosphor packed in cells of the obtained scintillator panel 11
had a grain boundary, and had a porosity of 0% and an average
particle size of 55 .mu.m. The luminance of the scintillator panel
11 was 140 in terms of a relative value where the luminance of the
scintillator panel 1 is 100. Thus, the scintillator panel 11
exhibited a good luminance although the luminance was slightly
lower as compared to Example 10. The scintillator panel 11 also
exhibited a good image sharpness.
Example 12
Except that in press-packing, the pressure was 50 MPa, and the
temperature was 25.degree. C., the same procedure as in Example 5
was carried out to prepare a scintillator panel 12, and evaluation
was performed.
The phosphor packed in cells of the obtained scintillator panel 12
had a grain boundary, and had a porosity of 20% and an average
particle size of 10 .mu.m. The luminance of the scintillator panel
12 was 105 in terms of a relative value where the luminance of the
scintillator panel 1 is 100. Thus, the scintillator panel 12
exhibited a good luminance although the luminance was lower as
compared to Example 5. The scintillator panel 12 also exhibited a
good image sharpness.
Example 13
Except that in press-packing, the pressure was 100 MPa, and the
temperature was 25.degree. C., the same procedure as in Example 5
was carried out to prepare a scintillator panel 13, and evaluation
was performed.
The phosphor packed in cells of the obtained scintillator panel 13
had a grain boundary, and had a porosity of 8% and an average
particle size of 20 .mu.m. The luminance of the scintillator panel
13 was 120 in terms of a relative value where the luminance of the
scintillator panel 1 is 100. Thus, the scintillator panel 13
exhibited a good luminance. The scintillator panel 13 also
exhibited a good image sharpness.
Example 14
Except that in press-packing, the pressure was 980 MPa, and the
temperature was 25.degree. C., the same procedure as in Example 5
was carried out to prepare a scintillator panel 14, and evaluation
was performed.
The phosphor packed in cells of the obtained scintillator panel 14
had a grain boundary, and had a porosity of 2% and an average
particle size of 25 .mu.m. The luminance of the scintillator panel
14 was 130 in terms of a relative value where the luminance of the
scintillator panel 1 is 100. Thus, the scintillator panel 14
exhibited a good luminance. The scintillator panel 14 exhibited a
relatively good image sharpness although the sharpness was slightly
deteriorated as compared to Example 5. The cause of the
deterioration of the image sharpness may be damage to a part of
barrier ribs due to packing at a high pressure.
Example 15
Except that NaI:TI was used as a phosphor, and the supply amount of
the phosphor in preparation of a press-molded film was 0.09
g/cm.sup.2, the same procedure as in Example 5 was carried out to
prepare a scintillator panel 15, and evaluation was performed.
The phosphor packed in cells of the obtained scintillator panel 15
had a grain boundary, and had a porosity of 3% and an average
particle size of 30 .mu.m. The luminance of the scintillator panel
15 was 130 in terms of a relative value where the luminance of the
scintillator panel 1 is 100. Thus, the scintillator panel 15
exhibited a good luminance. The scintillator panel 15 also
exhibited a good image sharpness.
Example 16
Except that SrI.sub.2:Eu was used as a phosphor, and the supply
amount of the phosphor in preparation of a press-molded film was
0.14 g/cm.sup.2, the same procedure as in Example 5 was carried out
to prepare a scintillator panel 16, and evaluation was
performed.
The phosphor packed in cells of the obtained scintillator panel 16
had a grain boundary, and had a porosity of 3% and an average
particle size of 30 .mu.m. The luminance of the scintillator panel
16 was 160 in terms of a relative value where the luminance of the
scintillator panel 1 is 100. Thus, the scintillator panel 16
exhibited a good luminance. The scintillator panel 16 also
exhibited a good image sharpness.
Comparative Example 1
Except that 0.11 g/cm.sup.2 of GOS:Tb was used as a phosphor, the
same procedure as in Example 1 was carried out to prepare a
scintillator panel 17, and evaluation was performed. The GOS:Tb
packed in cells of the obtained scintillator panel 17 had a grain
boundary, and had a porosity of 40% and an average particle size of
10 .mu.m. The luminance of the scintillator panel 17 was 70 in
terms of a relative value where the luminance of the scintillator
panel 1 is 100. Thus, the scintillator panel 17 was poor in
luminance. Since the scintillator panel 17 had a high porosity,
emitted light was excessively scattered, and thus the scintillator
panel 17 was also poor in image sharpness.
Comparative Example 2
0.11 g/cm.sup.2 of a CsI:Tl powder was supplied onto a base
material provided with grid-like barrier ribs, and was flattened by
a squeegee. Thereafter, the temperature was elevated to 630.degree.
C. under reduced pressure, so that the CsI:TI was melted, and
packed in cells to prepare a scintillator panel 18, and evaluation
was performed. The CsI:Tl packed in the cells of the obtained
scintillator panel 18 had no grain boundary, and had a porosity of
1.3%. The luminance of the scintillator panel 18 was 50 in terms of
a relative value where the luminance of the scintillator panel 1 is
100. Thus, the scintillator panel 18 was poor in luminance. The
barrier ribs were partially melted and deformed due to elevation of
the temperature to 630.degree. C., and therefore the scintillator
panel 18 was also poor in image sharpness.
Comparative Example 3
Except that in press-packing, the pressure was 5 MPa, and the
temperature was 25.degree. C., the same procedure as in Example 1
was carried out to prepare a scintillator panel 19, and evaluation
was performed.
The phosphor packed in cells of the obtained scintillator panel 19
had a grain boundary, and had a porosity of 30% and an average
particle size of 10 .mu.m. The luminance of the scintillator panel
9 was 60 in terms of a relative value where the luminance of the
scintillator panel 1 is 100. Thus, the scintillator panel 9 was
poor in luminance. Since the scintillator panel 19 had a high
porosity, emitted light was excessively scattered, and thus the
scintillator panel 19 was also poor in image sharpness.
From the above results, it is evident that the scintillator panel
according to the present invention contributes to marked
improvement of the luminance and image sharpness of a scintillator
panel in a radiation detector.
The present invention can be advantageously used as a scintillator
panel that forms a radiation detector to be used in a medical
diagnosis apparatus, nondestructive inspection equipment or the
like.
DESCRIPTION OF REFERENCE SIGNS
1: Radiation detector 2: Scintillator panel 3: Output substrate 4:
Substrate 5: Barrier rib 6: Phosphor layer 7: Barrier layer 8:
Photoelectric conversion layer 9: Output layer 10: Substrate 11:
Power supply unit 12: Light shielding layer 13: Reflecting layer
14: Protective layer
* * * * *